Make redis dependency optional

[ahesford]

The redis package is only used when somebody uses the redis cache handler, so the imports can be restructured to make redis an optional dependency.

[ahesford]

Ping

[stephanebruckert]

Great.

So this won't install redis by default, but is there anything that someone using redis should do to install it? Just wondering if there is anything we can document here

[Peter-Schorn]

We could catch the import error and display a detailed error message indicating that redis is an optional dependency and must be explicitly installed (clients often expect pip install -r requirements.txt to install all the dependencies for a package).

[ahesford]

For starters, I added a note to the readme in the latest commit.

[stephanebruckert]

We could catch the import error and display a detailed error message indicating that redis is an optional dependency and must be explicitly installed (clients often expect pip install -r requirements.txt to install all the dependencies for a package).

True, exceptionally for this use case of "connectors" we should go with the warning. @ahesford this is how a warning can be raised https://github.com/plamere/spotipy/blob/fa44fed76d7aecb70f9ee6cde14da5e2ce1e17d7/spotipy/client.py#L1951

For starters, I added a note to the readme in the latest commit.

Thanks that helps. Note that in any case we won't be able to merge this into v2 aka master just now, because it would break existing apps. So this will have to go into v3 https://github.com/plamere/spotipy/tree/v3
See #652
Can you please change the base of your PR from plamere:master to plamere:v3? Feel free to create a new PR if it gets messy

[ahesford]

Rebased on v3. That branch had no redis cache handler at all, so I brought the whole class over.

I added an import check during creation of a cache object to make sure redis is available and warn if not. I'm not sure there would be a good way to handle this in the functions where the import are actually needed, unless the exception catching is moved from RedisError to Exception to issue a blanket warning instead of hard errors for unexpected, non-redis failures.

[Peter-Schorn]

There's a typo here: "requied".

[Peter-Schorn]

Also, the word "required" may imply to some users that this module is required for the whole package. Instead, the error message should indicate that this module is required for the RedisCacheHandler.

[ahesford]

Fixed. I also restructured the history to preserve the evolution of Redis support on the master branch and diminish the extent of my own changes.